2 Sheffield Hallum University (2013) Changes in the Nutritional Content of Fruit and Vegetables During the Dehydration Process of Freeze Drying.

Freeze Drying

Freeze drying removes 99% of the moisture from food through a process called sublimation. Basically, this means that you can dry a frozen piece of broccoli by turning the ice crystals in the broccoli straight into a gas without melting it first. Feel like a physicist now?

Got it? No pressure. Well, maybe a little. You see, with a little pressure and just a small amount of heat the ice crystals start to break loose. A vacuum then sucks the air out of the freeze dryer to lower the pressure, enabling the ice crystals to turn into water vapor. The water vapor collects on freezing coils and the food is slowly and gently dried over several hours. That's why a freeze dried piece of broccoli still looks like broccoli, instead of a shriveled weed.